The present invention relates to a positional information system including an indoor positioning system complementary to the Global Positioning System (GPS).
Among positioning systems using electric waves, the most widely used system is the Global Positioning System (hereinbelow, referred to as “GPS”). In the GPS, utilizing GPS positioning signals transmitted from about 30 satellites on orbits around the earth, the positional relation between a receiver and the GPS satellite is measured, and the latitude, longitude and height of a current position are calculated. In the GPS, as a positioning signal from the satellite is used, positioning in indoor and underground space cannot be performed.
On the other hand, the Indoor Messaging System (IMES) using a positioning information transmission device for indoor positioning and a ground complementary signal is a positioning system to enable indoor positioning (see “Quasi-Zenith Satellite System Navigation Service Interface Specification for QZSS(IS-QZSS)” V1.1 Japan Aerospace Exploration Agency, Jul. 31, 2009 URL<http//qzss.jaxa.jp/is-qzss/index_e.html>). The ground complementary signal (IMES signal) uses the same message structure as that of a satellite positioning signal. In this system, in place of satellite orbit data (navigation message), positional information indicating the installation site of the positioning information transmission device is transmitted. Unlike general GPS positioning, the positioning by reception of the IMES signal is an extremely simple and easy positioning method because the position can be specified by merely decoding/decrypting positional information indicating the installation site of the positioning information transmission device superimposed on the IMES signal. According to this method, indoor positioning can be realized by very small-scale modification even with existing GPS receivers or various terminals with GPS reception function. By virtue of such high interoperability with the satellite positioning, the indoor positioning system using the positioning information transmission device for indoor positioning and the ground complementary signal attracts attention as a promising system and is the focus of research and development.